Thermostatic switch of the remote resetting type



J. R. GELZER Aug. 16, 1966 THERMOSTATIC SWITCH OF THE REMOTE RESETTING TYPE Filed June 18, 1964 IIiY ENTOR. L ZlZf BY I United States Patent 3,267,237 THERMOSTATIC SWITCH OF THE REMOTE RESETTING TYPE John R. Gelzer, Barrington, Ill., assignor to Littelfuse, Incorporated, Des Plaines, 111., a corporation of Illinois Filed June 18, 1964, Ser. No. 376,098 7 Claims. (Cl. 200-122) This invention relates to an improved overload protection thermostatic switch of the remote resetting type having an insulating base which carries a stationary contact and a thermostatic member provided with a movable contact normally engaging the stationary contact at a predetermined temperature value of the thermostatic member. Thermostatic switches of this type usually are provided with a heating element connected across the switch contacts and which, under an overload condition in the circuit which opens the contacts, limits current flow in'the circuit and provides sufiicient heat to maintain the contacts in an open position. When the abnormal condition in the circuit has been remedied or relieved, and the circuit is momentarily open by a remote switch to cause the limited current to cease flowing in the heater element, the contacts re-engage to permit current to flow through the circuit.

Heretofore, overload protection thermostatic switches of the type wherein the heating element was placed in parallel with the contacts, were limited to use in low voltage circuits where relatively high currents were involved. In circuits of this character, low values of heating element resistance were capable of providing the heat required to keep the contacts open. However, in circuits of higher voltage, where the necessary heating element resistance becomes comparatively high, it was not readily possible with previously manufactured overload protection thermostatic switches to obtain resistance values of sufficient magnitude to provide the heat required to maintain the contacts in an open position. This inherent shortcoming of heretofore manufactured overload protection thermostatic switches substantially restricted their utilization to low voltage circuits which excludes the commercial power line voltages of 110-220 volts.

Another disadvantage of overload protection switches as heretofore manufactured is that they did not structurally lend themselves to automatic assembly and calibration techniques.

It is an object of the present invention to provide an improved remote resetting overload protection thermostatic switch having utility in high voltage circuits, such as commercial llO-220 volt circuits.

It is also an object of the present invention to provide an improved overload protection thermostatic switch which is compact in size and can be completely automatically assembled and calibrated.

It is another object of this invention to provide an improved overload protection thermostatic switch which is manufactured from a relatively few, simple, inexpensive, standardized parts.

Other objects, advantages and features of this invention will become apparent as the description proceeds.

Briefly, the improved overload protection thermostatic switch of this invention comprises an insulating base having spaced terminal assemblies of unique construction secured thereon. Each terminal assembly includes a terminal member which acts not only as a terminal to which conductors can be soldered, but as a support for a stationary contact or movable thermostatic member and as a clip for a heater element. To that end, each terminal member is fabricated from a single die stamping to provide a circuit connecting portion, a table-like mounting platform or portion, and opposed, resilient extensions forming an open-ended heater element retaining bracket or clip thereon. A stationary contact is carried on the mounting platform or portion of one of the terminal members and a bimetallic thermostatic member having a movable contact normally in engagement with the stationary contact is carried on the corresponding portion of the other terminal member. The terminal member carrying the thermostatic member is uniquely shaped to permit easy automatic calibration of the overload protection thermostatic switch by a unique weight calibration technique.

A heater element or coil, in the form of a resistor, advantageously is releasably carried by the heater element retaining clips of the terminal members. The heater element desirably has a film or coating of a resistance-forming material thereon in contact with the electrical circuit through the retaining clips of the terminal members. The surface of the heater element is provided with a helically shaped groove along a portion of its length to be located adjacent a portion of the thermostatic member and which functions to concentrate the heat at the appropriate place and to provide in a short space the relatively large resistance required. The heater element is connected in parallel with respect to the contacts of the overload protection thermostatic switch. The resistance values of the heater element can be varied by simply altering the number and/ or spacing of the turns or convolutions of the grooves in the conductive coating or film carried on the surface thereof.

The insulating base has terminal-receiving openings into which the terminal assemblies can be dropped from the top of the base where the terminal member of the assembly, including the thermostatic member, pivots on the base to a degree proportional to a calibrating weight which is dropped on the thermostatic member. The insulating base has cement-receiving wells in the top of the base opening'into the terminal-receiving openings. Cement is poured into the wells and hardened to fix the relative weight adjusted positions of the terminal members. The relative angular position of the terminal member carry- I ing the stationary contact and the movable contact on the thermostatic member determines the contact pressure for the calibration conditions of the switch and so determines the temperature (current level) at which the switch opens.

The assembly of the switch is completed by snapping the heater tube on the terminal clips and dropping a cover onto the base and securing the cover to the base. The design of the switch just described enables the switch readily to be machine assembled and calibrated from only a few basic sub-assemblies.

In order that the invention may be fully understood,

' reference will now be made to the drawing wherein an exemplary embodiment of the overload protection thermostatic switch of the present invention is illustrated, it being understood, however, that variations both in construction and in material may be made without departing from the scope of the invention.

In the drawing,

FIG. l'is a view in perspective of an embodiment of the overload protection thermostatic switch of the invention;

FIG. 2 is a vertical sectional view taken substantially along line 2-2 of FIG. 1;

FIG. 3 is a vertical sectional view taken substantially along line 3-3 of FIG. 2;

FIG.. 4 is a horizontal sectional view taken substantially along line 4-4 of FIG. 2;

FIG. 5 is a view in perspective of an embodiment of one of the terminal members of the switch of FIG. 1; and

FIG. 6 is a transverse section through the insulating base with all of the switch components removed therefrom.

' .3 Referring now to FIG. 1 of the drawing, one form of the invention is generally designated at 10. It includes an insulating base 12 which is substantially rectangular in .shape and which may be formed from a heat resistant,

'sides of the base 12 and bent or crimped inwardly to engage the outer surface 20 of the base. The length and width of the cap or housing 14 are slightly less than the corresponding dimensions of the base 12. Thus, when the cap or housing 14 is fixed in position on the base 12, the margins of the open end of the cap or housing 14 rest on the inner surface 22 of the base 12. The cap or housing 14 desirably has mounting tabs or extensions 24-24 which, in the embodiment illustrated, conveniently are struck from an end and top wall thereof.

The base 12 is provided with a pair of off-center openings 26 and 26' which extend through integral, outwardly extending bosses 3030 on the outer surface 20 of the base 12. The openings 26 and 26' preferably are countersunk at the inner face 22 of the base 12 to form elongated, transverse, recesses 3232 on one side of the openings which extend partway through the base, and trough-like cement-receiving wells 33-33 on the other 'side of the openings. See FIG. 6.

The overload protection thermostatic switch further includes terminal assemblies 36 and 38 which are suitably held in the openings 26 and 26, respectively, of the base 12. The terminal assemblies 36 and 38, advantageously include terminal members 37 and 39 which may be made by a diestamping operation. The terminal member 37 has avertically extending lower body portion 37a and a platform portion 37b at the tip thereof. The body portion 37a has an opening 44 for receiving a lead wire from a circuit and a longitudinal rib 48 which fits into a recess 32 in the base 12 when the terminal assembly 36 is secured in the terminal-receiving opening 26. The wider upper section of the body portion 37a is wider than the lower section and a horizontal transverse shoulder 49 is formed thereby which rests on the flat top of the insulatingbase 12. The platform portion 37b has a contact receiving opening 52 therein. The terminal member 37 further includes an open-ended clip portion 37c joined to the platform portion37b by an outwardly extending arm 56. The clip portion 37c comprises opposed, resilient extensions 5858 having outwardly diverging end portions 60-60 which are joined at their inner margins to outwardly curved socket-forming portions 6262.

hereinafter, the angulation of the shoulder or edge 72 performs an important function in the calibration of the preferred embodiment of the overload protection thermo- 7 static'switch of this invention.

The platform portions 37b and 39b of the terminal I members 37 and 39 carry the. stationary and movable The terminal member 39 essentially is similar in many respects to the terminal member 37, and has a lower body portion 39a having an opening 44' and a longitudinal rib 48', an upper platform portion 39b, and a clip 39c joined to the platform portion 39b by an arm 56'. The

clip portion 390 has opposed, resilient extensions 58'58 ondly, whereas the wider upper section of the body portion 37a of the terminal member 37 has a horizontal downwardly facing shoulder 49, the 'wider upper section of the bodyportion 39a of the terminal member 39 has an inclined downwardly facing shoulder or edge 72, forming an obtuse angle with the adjacent margin edges 73 and 74 of the terminal member 39. As will be made clear contacts of the switch. Thus, a stationary contact is secured, as by riveting, in the opening 52 in the platform portion 37b of the terminal member 37. A thermostatic member in the form of a bimetal blade 82 is secured as by welding to the dimple 66 on the raised section 64 of the platform portion 39b of the terminal member 39. The. bimetal blade 32 has a relatively Wide bimetallic compensator portion 84 anchored to the dimple 66 and having its low expansion side 86 on the bottom thereof and a relatively narrow bimetallic free end portion 88 having its low expansion side 90 on the top thereof. The dimple 66 raises the wide compensator portion 84 of the bimetal blade 82 from the platform portion 39b and thus permits the bimetal blade 82 to flex freely. The free end portion of the bimetal blade 82 has a movable contact 92 secured thereto as by welding or the like. The size and material of the bimetal blade are selected in accordance with the proposed current rating of the overload protection thermostatic switch. V a In calibrating the overload protection thermostatic switch of the preferred form of this invention, the termi: nal assembly 36 including the terminal member 37 and the stationary contact 80 secured thereon, and the terminal assembly 38 including the terminal member 39 and the bimetal blade 82 secured thereto are firstvmounted on the insulating base 12 by inserting the lower sections of the terminal members 37 and 39 into the insulating base openings 26 and'26' so that the movable contact 92 rests on the stationary contact 80. As clearly shown in FIG. 2, the downwardly facing horizontal shoulder 49 of the terminal member 37 rests against the horizontal top or inner surface 22 of the base 12 which establishes a fixed orientation for the terminal member 37. The inclined,

downwardly facing shoulder 72 of the terminal member 39, however, makes a point contact with the edge of the associated base opening 26' which provides sufiicient clearance for the terminal member 39 so that the latter can pivot in the plane of the bimetal blade. This characteristic is utilized in the calibration of the over load protection thermostatic switch 10. After the terminal members 37 and 39 are so positioned in the openings 26 and 26' of the insulating base 12, a calibrating weight is applied to the central portion of the bimetal blade 82 which flexes the same and causes the terminal member 39 to tilt in a counterclockwise direction to a degree depending on the magnitude of the weight. The final pressure between the contacts 80 and 92 for a given current in the blade is determined by the weight adjusted angle of the terminal member 39.

A suitable liquid, hardenable cement 94, such as an epoxy cement or the like, is poured into the trough-like countersunk openings 3333, and while the calibrating weight remains on the bimetal blade, the cement is hardened to fix the weight-adjusted position of the terminal member 39 and to anchor the terminal member to the base 12.

Assembly of the overload protection thermostatic switch is completed by mounting a heater element on the switches which are electrically connected across the contacts 80 and 92. In the particularly preferred aspects of the present invention, this is achieved simply by snapping the ends of a substantially cylindrical, small diameter, resistor into the socket-forming portions 6262 and 62'-62' on the clips 54 and 54' of the terminal members 37 and 39'. The resistor 100 desirably takes the form of a rod of a nonconductive material, such, for example, as glass, having a loW coefiicient of thermal expansion. The rod of nonconductive material has a coating of a resistance forming material deposited on its outer surface which establishes the necessary electrical contact across the clips 37c and 39c. In the embodiment of the invention illustrated, formation of the resistor 100' conveniently is accomplished by coating a glass rod with tin oxide or the like. To enable the resistor 100 to generate the amount of heat necessary to maintain the bimetal blade 82 in a flexed position when an overload condition occurs in a circuit in which the overload protection thermostatic switch is utilized, the coating is provided with an unbroken helical or spiral groove 101 at a predetermined point along its length which will be adjacent the free end portion 88 of the bimetal blade 82. The spacing and number of convolutions or turns forming the groove 101 can be varied within wide limits to establish the desired heat'generating properties of the resistor 100. The versatility of the resistor 100 in this regard permits concentration of the heat generated by it under circuit overload conditions at a particular preselected portion of the bimetal blade 82.

When the bimetal blade 82 is placed in varying environments at different temperatures, the compensator portion 84 of the bimetal will flex in one direction and the free end portion 88 thereof will flex in the opposite direction so that the movable contact 92 will in effect remain in the same position and will bear down on the stationary contact with the same pressure for a given current flowing through the bimetal blade. Since the compensator portion 84 of the blade 82 is much wider than the free end portion 88, it has a much lower resistance and so most of the heat developed by flow of current in the blade will occur in the free end portion 88 thereof so that the position of the movable contact 92 or the pressure thereof against the stationary contact 80 will vary with the current flowing through the blade.

The overload protection thermostatic switch of the present invention can be used to advantage in low current circuits at commercial power line voltages, such as 110-220 volts. Generally speaking, these switches have current ratings of from about 1 to about 5 amperes, and will open at current overloads approximately 1 /2 times that of the normal current rating thereof. Resistors employed in switches of this character usually have a rating of from about 6,000 to 10,000 ohms. Overload protection thermostatic switches .of this invention, having the indicated electrical properties, have been made approximately 1 /2 to 2 inches long, about /2 to 4 inch wide, and, as measured from the top wall of the housing or cap 14 thereof to the bottom of the terminal members 37 and 39, approximately 1 to 1 /2 inches high. Except for the important, but minor, modifications hereinabove described, the parts of the overload protection thermostatic switch are, for all practical purposes, standardized and particularly adaptable to assembly by automatic equipment.

While for the purpose of illustrating and describing the invention, a specific embodiment has been shown, it is to be understood that modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A thermostatic switch assembly comprising: an insulating base, spaced terminals secured to said base for connecting the switch in an electrical circuit, said terminals each having an open-ended clip physically and electrically connected thereto, a stationary contact carried by one of said terminals, an electrically conductive heat responsive bimetallic mern ber carried by the other of said terminals and having a contact thereon normally engaging said stationary contact, and a heating element releasably held in the clips of said terminals and spaced from said bimetallic member, said heating element acting electro-thermally to maintain said contacts in an open position when an overload condition occurs in said electrical circuit.

2. A thermostatic switch assembly comprising: an insulating base, spaced terminals secured in said base, said terminals having a circuit engaging portion for connecting the switch in an electrical circuit, said terminals further having a mounting portion and opposed, resilient extensions forming an open-ended clip thereon, a stationary contact carried on the mounting portion of one of said terminals, a thermostatic element carried by the mounting portion of the other of said terminals and having a movable contact thereon normally engaging said stationary contact, and a resistor releasably carried by the clips of said terminals, said resistor being connected in parallel with respect to said contacts and carrying an electrically conductive material in contact with said terminals, said resistor acting thermoelectrically to maintain said contacts in open position when an overload condition occurs in said electrical circuit.

3. A thermostatic switch assembly comprising: an insulating base, spaced terminals secured in said base, said terminals having means for connecting the switch in an electrical circuit, said terminals further having resilient, opposed portions forming resilient-open-ended holding means thereon, a stationary contact carried by one of said terminals a thermostatic element carried by the other of said terminals having a movable contact thereon normally engaging said stationary contact, and means releasably retained in said open-ended holding means having deposited thereon an unbroken, electrically resistive material in contact with said terminals, said last mentioned means acting to maintain said contacts in an open position when an overload condition occurs in said electrical circuit.

4. A thermostatic switch assembly comprising: an insulating base, spaced terminals secured in said base for connecting the switch in an electrical circuit, said terminals each having an integral, resilient, open-ended clipphysically attached and electrically connected thereto, a stationary contact carried by one of said terminals, a thermostatic element carried by the other of said terminals having a movable contact thereon norm-ally engaging said stationary contact, a heating element releasably engaged in the clips of said terminals having deposited thereon an electrically resistive material in contact with said terminals, said heating element having 'a continuous helical groove in the conductive material thereof and acting electrothermally to maintain said contacts in an open position when an overload condition occurs in said electrical circuit, and a housing for said switch assembly.

5. A thermostatic switch comprising: an insulating base having an upper surface with .a pair of spaced, vertical terminal-receiving openings extending through the base, a bimetal blade and terminal assembly including a first terminal member having a portion mounted in one of said openings, a stationary contact and terminal assembly including a second terminal member having a portion mounted in the other of said openings, said first and second terminal members each having a mounting portion and a clip portion physically attached and electrically connected thereto, a flexible ambient temperature compensated responsive bimetal blade extending generally transversely from the mounting portion of said first terminal member and having a relatively low resistance compensating base portion and a relatively high resistance free end portion with a movable contact thereon, a stationary contact on the mounting portion of said second terminal member normally in engagement with said movable contact, and a heating element engaged with the clip portion of each of said terminal members, said heating element having a resistance forming material on the outside thereof, the area of highest resistance of said material being positioned proximal to the relatively high resistance free end portion of said bimetal blade, whereby said blade will be caused to flex sufiiciently to maintain said contacts in an open position when the switch is activated.

6. A thermostatic switch assembly comprising: an insulating base having an upper surface with a pair of spaced, vertical terminal-receiving openings extending through the base, a bimetal blade and terminal assembly including a first terminal member having a portion mounted in one of said openings and having an integral electrically conductivemounting portion and a heating element-retaining portion and a flexible temperature responsive bimetal blade secured to the mounting portion of said terminal member having a free end portion with a movable contact thereon, said first terminal member further having pivot-forming shoulder means abutting an edge portion of its terminal-receiving opening at the upper surface of said base, a stationary contact and terminal assembly including a second terminal member having a portion mounted in the other of said openings and having an integral electrically. conductive mounting portion and heating element-retaining portionand carrying a stationary contact on the mounting portion thereof which normally is in engagement with said movable contact, said second terminal member further having horizontal down- Wardly facing shoulder means abutting the upper surface of said base, and a heating element releasably held in the retaining portions of said terminal members in spaced relation with respect to said bimetal blade, said heating element acting electrothermally to maintain said contacts in an open position when said switch assembly is activated.

7. A thermostaticv switch assembly comprising: an insulating base having an upper surface with a pair of spaced, vertical terminal-receiving openings extending throughthe base and cement-receiving Wells respectively on the top of the base opening onto said terminal-receving openings, a bimetal blade and terminal assembly ineluding a first terminal member having a portion mounted on one of said openings and having an integral electrically conductive mounting portion and heating element-retaining portion and a flexible temperature responsive bimetal 8 blade securedto themounting portion of said terminal member having a free end portion with .a movable contact thereon, said first terminal member, further having pivotforming shoulder means abutting an-edge portion of its terminal-receiving opening at the upper-surface of said base, a stationary contact and terminal assembly includ-' ing a second terminal member having a portion mounted inthe other of said openings and having an integral electrically conductive mounting portion and heating element-' References Cited by the Examiner UNITED STATES PATENTS 1,394,055 10/1921 White 33s 332 2,403,803 9/1946 Kersley 200 122 2,745,924 5/1956 Coates 200-138 3,143,619 8/1964 Hummel 200 13s FOREIGN PATENTS 582,677 11/1946 Great Britain.

ERNA D A. GILHEANY, Primary Examiner.

L. A. WRIGHT, Assistant Examiner. 

1. A THERMOSTATIC SWITCH ASSEMBLY COMPRISING: AN INSULATING BASE, SPACED TERMINALS SECURED TO SAID BASE FOR CONNECTING THE SWITCH IN AN ELECTRICAL CIRCUIT, SAID TERMINALS EACH HAVING AN OPEN-ENDED CLIP PHYSICALLY AND ELECTRICALLY CONNECTED THERETO, A STATIONARY CONTACT CARRIED BY ONE OF SAID TERMINALS, AN ELECTRICALLY CONDUCTIVE HEAT RESPONSIVE BIMETALLIC MEMBER CARRIED BY THE OTHER OF SAID TERMINALS AND HAVING A CONTACT THEREON NORMALLY ENGAGING SAID STATIONARY CONTACT, AND A HEATING ELEMENT RELEASABLY HELD IN THE CLIPS OF SAID TERMINALS AND SPACED FROM SAID BIMETALLIC MEMBER, SAID HEATING ELEMENT ACTING ELECTRO-THERMALLY TO MAINTAIN SAID CONTACTS IN AN OPEN POSITION WHEN AN OVERLOAD CONDITION OCCURS IN SAID ELECTRICAL CIRCUIT. 